Conventionally, there is known a power conversion device such as a PFC (Power Factor Correction) circuit (for example, see Non-Patent Document 1).
The PFC circuit of Non-Patent Document 1 includes a bridge circuit, a high-frequency filter provided on an AC side of the bridge circuit, a reactor provided between the bridge circuit and the high-frequency filter, a smoothing capacitor provided on a DC side of the bridge circuit, a snubber capacitor provided between the bridge circuit and the smoothing capacitor, and a backflow prevention diode provided between the smoothing capacitor and the snubber capacitor. In the PFC circuit, a three-phase AC power supply is connected onto an input side, and a load is connected onto an output side.
Three legs constructed with upper arms and lower arms are provided in the bridge circuit. A switch element is provided in each arm (upper arm and lower arm), and a diode is connected in parallel to the switch element. In the bridge circuit, the switch element of the upper arm or lower arm in each leg is selected according to a phase of an AC voltage (input voltage), and the three selected switch elements are driven at a constant duty ratio. The PFC circuit operates in a DCM (Discontinuous Current Mode), and current is discontinuously passed through the reactor.
In the PFC circuit of Non-Patent Document 1, the switch element of the bridge circuit is turned off when the current is not passed through the reactor, thereby performing ZCS (Zero Current Switching). In the PFC circuit, the switch element of the bridge circuit is turned off while the snubber capacitor is discharged, thereby performing ZVS (Zero Voltage Switching). Therefore, a switching loss can be reduced.